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Indentation test to determine the fracture toughness of nickel phosphorus coatings

type de publication      article dans une revue internationale avec comité de lecture
date de publication 2002
auteur(s) Roman Adriana; Chicot Didier; Lesage Jacky
journal Surface and Coatings Technology
volume (numéro) 155 (2-3)
pages 161 – 168
résumé In this paper, Vickers indentation was used to study the resistance to cracking of electroless nickel phosphorus coatings. For low indentation loads, craking initiates only at the tips of the indent (primary cracking). It was shown that these cracks are of the Palmqvist type. For higher loads, new cracks, for wich initiation sites are located on the edges of the indent, begin to form (secondary cracking). It was found that this change in the cracking mechanism occurs when the primary cracks reach the interface with the substrate. This result shows that the interface resistance to cracking is higher than the cohesion of the coating. In addition, it was possible to apply the same formulae whatever the cracking process, if the total number of cracks was divided by 4, like for the first cracking process. Values of fracture toughness Kc=1.5MPa m1/2 for a 300°C treatment and 2.1 MPa m1/2 for a 600°C treatment were found, independent of the coating thickness.
mots clés Hardness; Fracture toughness; Nickel phosphorus; Coating
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